Method and apparatus for well control



Oct. 26, 1965 R. RECORDS METHOD AND APPARATUS FOR WELL CONTROL 2Sheets-Sheet 1 Filed Sept. 13, 1962 100M fl. is cord:

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I j rrazzva n- Oct. 26, 1965 R. RECORDS METHOD AND APPARATUS FOR WELLCONTROL 2 Sheets-Sheet 2 Filed Sept. 13, 1962 INVENTOR. WW ma k BY %a@666% A TfOfi/Vf/J United States Patent Ofl ice 3,213,939 Patented Oct.26, 1965 3,213,939 METHOD AND APPARATUS FOR WELL CONTROL Louis R.Records, Lafayette, La., assignor, by mesne assignments, to DrillingWell (Iontrol, Inc, Houston, Tex., a corporation of Texas Filed Sept.13, 1962, Ser. No. 223,459 12 Claims. (Cl. 166-8) This invention relatesto a method and apparatus for well control, and more particularly itrelates to such a method and apparatus for maintaining control of a wellduring the drilling operation to prevent blowing out of the well.

It is customary during the drilling of a well to pump or circulate adrilling fluid, known in the art as mud, downwardly through the drillpipe or stem to which the drill bit is attached and into the annulusformed by such drill stem and the wall of the well bore whereupon suchmud is returned to the surface. There is thus created what might betermed a U-tube with the drill stem forming one leg of the U-tube andthe annulus between the drill stem and the wall of the well bore formingthe other leg.

The drilling fluid or mud functions, in effect, as a stopper in the wellsince it exerts a hydrostatic pressure on the bottom of the wellaccording to the specific weight of the mud thereabove, and thehydrostatic pressure of each of the mud columns must balance or overcomethe formation pressure in order to prevent blowouts, that is, theblowing or forcing of the mud out of the well bore and the venting ofthe formation pressure to the atmos phere. However, the pressure of theformation adjacent the drill bit, or bottom-hole pressure, must also beconsidered because this pressure must sustain the hydrostatic pressureof the mud in order to prevent loss of circulation, that is, the loss ofmud as it escapes into a formation due to the pressure exerted by themud column. It is therefore desirable that the pressures in the wellbore adjacent the drill bit remain in a more or less balanced condition.

However, as the drilling of the well progresses, the drill bitfrequently passes through a formation or zone wherein the pressure isincreased to such an extent that an unbalanced pressure condition in thewell occurs. When such an unbalanced pressure condition exists in thewell, there is created the danger of a blowout unless the increasedpressure is balanced or overcome and control of the well is maintained.The material in the high pressure formation, which is usually gas, oil,salt water, or the like, escapes from the formation under the increasedpressure into the well bore thereby reducing the specific weight of themud therein, and increasing the danger of a blowout. Also, if gasescapes from a high pressure formation, it becomes entrained in the mudstream and tends to expand as it travels out of the well and passesthrough a flow device, such as a throttling valve or choke, thereby increasing the abrasive action of the mud stream and subjecting the flowdevice to excessive wear.

It has been the practice in the past, when blowout conditions areencountered, to slug the well, that is, a mud having a weight greaterthan that of the inadequate mud already present in the Well is pumpedinto the well in an attempt to prevent the blowout and maintain controlof the well. This procedure is not satisfactory since the well is notcontrolled during the slugging operation and the blowout may occurbefore the adequate or proper mud is circulated into the well and it isbrought under control again. Another disadvantage of this practice isthat the well may be over-pressured by the heavy mud column with theresulting loss of circulation.

It is, therefore, an object of this invention to provide a method andapparatus for conveniently restoring and maintaining the balancedpressure conditions which are necessary to maintain the well undercontrol during the drilling operation.

It is another object of this invention to provide a method and apparatuswhich involves maintaining a desired back pressure on the drilling fluidor mud by means of a controlled gas pressure, which pressure togetherwith the column of otherwise inadequate drilling fluid, will assure thata blowout is prevented.

It is another object of this invention to provide a method forcontrolling a well during actual or threatened blowout conditions byapplying a controlled back pressure to the drilling mud so that saidpressure plus the hydrostatic pressure of the mud is suflicient toprevent a blowout, after which mud of proper weight is added to bringthe well back into the desired pressure balance, said back pressurebeing gradually reduced as mud of the desired weight is added andbalanced pressure conditions in the well are restored.

Another object of this invention is to provide an apparatus forcontinuously removing the gas entrained in the drilling mud whilecontinuously circulating said mud whereby the abrasive action of the mudis materially reduced and yet there is little or no settling out of thematerials or cuttings contained within such mud.

Still another object of this invention is to provide an apparatus forseparating or removing the gas entrained in the mud before such mud ispassed through a flow device, such as a valve or choke, therebysubstantially removing the abrasive action of the mud as it passesthrough such flow device.

A further object of this invention is to provide a method and apparatusof the character described wherein the mud is passed through a first gasseparating unit and may thereafter be subjected to subsequent stageseparation under reduced pressure conditions to assure completeseparation or removal of the gas from the mud.

Yet another object of this invention is to provide an apparatus of thecharacter described which may be initially charged with a gas, such asnitrogen, to the desired back pressure for maintaining control of thewell.

The construction designed to carry out the invention will be hereinafterdescribed, together with other features thereof.

This invention will be readily understood from a reading of thefollowing detailed description and reference to the drawings wherein:

FIGURE 1 is a diagrammatic illustration of a well connected to or withan apparatus for maintaining a desired back pressure on said well andfor removing entrained gas from the drilling fluid, and

FIGURE 2 is an elevation view, partly in section, diagrammaticallyillustrating such an apparatus together with a second similar apparatusfor removing gas from r the mud stream under reduced pressureconditions.

In the drawings, the numeral 10 designates a well bore having the usualdrill pipe or string 11 disposed therein. The drill string 11 issuspended from the surface of the well by the well-known drilling rig(not shown). The drill bit 12 is attached to the bottom end of the drillpipe 11 in the usual manner.

A pump 13 draws the drilling fluid or mud from a suitable storage vesselor pit 14 through the conduit 15 and pumps it into the discharge line 16which communicates with the drill pipe 11. The mud passes downwardlythrough the drill pipe 11, outwardly through the drill bit 12 and intothe annulus 17 formed between the exterior of the drill pipe 11 and thewall 18 of the well 10. A suitable conduit 19 communicates with theupper end of the annulus 17 below the conventional blowout preventerenclosed within and forming a part of the casinghead and provided forpacking off the annulus space around the drill pipe 11 in the event ofthreatened blowout. The conduit 19 constitutes an outflow line forreturning drilling mud and any entrained well fluid and discharges intothe apparatus A which functions to maintain a desired back pressureagainst the drilling fluid in the annulus 17. As will be more fullyexplained, the apparatus A also provides a means for removing entrainedgas, if any, from the mud. Suitable valves 21 and 22 are disposed withinthe lines 16 and 19, respectively, so that the well may be shut in byclosing said valves.

The apparatus A includes a vessel having a mud discharge line 23communicating with the lower portion of such vessel, and a flow controlvalve 24 is provided in the line 23 to control the flow of mudtherethrough. The opening or flow passage through the valve 24 iscontrolled by a liquid level control means 25, such as a float 25aactuating a pneumatic system for opening or closing the valve 24according to the level of the mud within the vessel 20. It is thusapparent that the level of the mud within the vessel 20 is maintained ata more or less constant level or within certain limits depending uponthe adjustment and operation of the particular liquid level controlmeans employed. The mud discharging through the line 23 and valve 24 isordinarily conveyed to the pit 14 or some other suitable storage vessel.As will be more fully described hereinafter, the mud may be subjected tosubsequent stage or low pressure gas separation.

A gas discharge line 26 communicates with the gas space in the upperportion of the vessel 20 above the level of the mud. A means formaintaining a back pressure, such as the valve 27, is provided in thegas line 26 so that a desired back pressure may be maintained on thevessel 20, line 19 and annulus 17. Such a back pressure is maintained bythe valve 27 by permitting a certain amount of the gas to escape or ventfrom the interior of the vessel 20, and the back pressure thusestablished may be varied by varying the opening through the valve 27 orthe time during which it stays open. The gas which is entrained in themud escapes therefrom into the gas space and gas discharge line 26wherein it may be conveyed a safe distance from the well and flared. Itis to be noted that the mud discharge valve 24 cooperates or coacts withthe gas discharge valve 27 in maintaining the back pressure; however, itis preferable to establish a more or less constant mud level within thevessel 20 and adjust and maintain the desired back pressure by means ofthe gas valve 27.

There is also provided a means for charging the vessel to the desiredback pressure, and this means preferably includes a storage vessel 28for storing the charging gas, such as nitrogen, and a line 29communicating between the storage vessel 28 and the gas space Within thevessel 20. A valve 30 is provided in the line 29 so that the connectionbetween the storage vessel 28 and the vessel 20 may be broken or shutoff when the desired pressure is reached in the vessel 20. By providinga suitable pressure responsive valve in lieu of the valve 30 in the line29, the pressure charging means may also function to make up any suddenpressure loss in the vessel 20 below the desired pressure.

It is noted that the apparatus A need not be connected to the well atall times during the drilling operation, but it may be held readilyavailable on a standby basis so that it may be connected to the well inthe manner described when desired.

In the use of the apparatus or system which provides a method ofsequential steps for properly maintaining control of the well andthereby preventing a blowout, the apparatus does not functioin duringnormal drilling operations at which time the valves 21 and 22 are opento permit normal circulation of the drilling fluid in the wellknownmanner. However, when blowout conditions are encountered during thedrilling operation, it is preferable to first shut in the well byclosing the valves 21 and 22 so that the well is contained and theimmediate danger of a blowout is eliminated. The apparatus A may then beconnected to the well and charged to the desired back pressure tobalance or overcome the increased pressure in the well. Thereafter, thevalves 21 and 22 are opened and drilling fluid of the desired specificweight is pumped into the drill stem 11 While the desired back pressureis maintained on the annulus 17 to prevent a blowout through suchannulus. As the desired mud is pumped into the drill pipe 11, itdisplaces the mud in the drill pipe 11 and annulus 17; such mud beingdischarged through the line 19 into the vessel 20. It is thus apparentthat the well is maintained under control at all times through thereadily controllable back pressure applied to the well, and it is notnecessary to slug the well with a heavy mud since the desired mud may becirculated into the well at the desired rate without any danger ofoverpressuring the well.

If salt water has been forced into the mud by the increased formationpressure, then the mixture of mud and salt water simply passes throughthe apparatus A while such apparatus maintains the desired back pressureon the annulus 17. However, if gas has been forced into the mud by theincreased formation pressure, then substantially all this entrained gasis separated from the mud stream in the vessel 20 and escapes throughthe gas discharge line 26 and the back pressure valve 27. The gasseparated or released from the mud stream displaces the initial charginggas, such as nitrogen, so that the separated gas is utilized formaintaining the desired back pressure on the well.

The mud discharging from the vessel 20 through the line 23 and muddischarge valve 24 is substantially gasfree and the valve 24 istherefore subjected to less abrasion and wear than it would be had theentrained gas not been removed from the mud. It is noted that the mudpasses through the vessel 20 in a substantially continuous manner sothat there is little or no time in which the materials carried by orsuspended in the mud, such as cutting or lost circulation material, maysettle out.

The pumping of the desired mud into the drill pipe 11 is continued untilthere is a column of mud of the desired specific weight within the drillpipe sufficient to create a hydrostatic pressure to balance or overcomethe increased formation pressure. Thereafter, continued pumping forcesthe mud of the desired specific weight into the annulus 17. As thehydrostatic pressure created by the mud column in the annulus 17increases, the back pressure maintained on such annulus by the apparatusA is reduced so that the formation pressure is contained and the well isunder control at all times, and yet the danger of loss of circulation isreduced or eliminated. Circulation of the desired mud into the annulusis continued until there is established therein a column of mud whichexerts a hydrostatic pressure suflicient to balance or over come theformation pressure and the need for the back pressure no longer exists.Thus, the balanced pressure condition in the well is restored so thatthe danger of a blowout is eliminated, and the drilling operation mayproceed.

In summary, a back pressure is applied to the well by imposing such backpressure on what might be termed the annulus leg of a U-tube so that ablowout therethrough is prevented. Thereafter, a hydrostatic pressuresufficient to contain the increased formation of pressure is created bya column of mud of the desired specific weight in the drill pipe leg ofthe U-tube so that a blowout may not occur therethrough. Continuedpumping of such mud will circulate it into the annulus leg so that asimilar hydrostatic pressure is created therein as the back pressure isreduced so that a blowout through the annulus leg is prevented. Balancedpressure conditions are maintained in the well at all times so that thedanger of a blowout is eliminated, and yet it is not necessary toover-pressure or slug the well with an excessively heavy mud which mayresult in an undesirable loss of circulation.

As has been noted, it is frequently desirable to provide subsequent lowpressure separation for removing whatever gas may remain in the mudafter it has passed through the vessel 20, and a second or low pressureseparator is illustrated in FIGURE 2. As shown in this figure, theapparatus A heretofore described, which functions as the first or highpressure separator is illustrated and the low pressure or second stageseparator is connected in series therewith. The low pressure separatoris similar to the apparatus A previously described in that it includes avessel 120 having a gas discharge line 126 and back pressure valve 127,mud discharge line 123, and a mud discharge control valve 124 which isactuated by a liquid level control means 125 whereby the liquid level inthe vessel is maintained more or less constant or within certain limits.A means for initially charging the second stage vessel 120 to a desiredback pressure is also provided, and such means preferably includes acharging line 129 communicating with the storage vessel 28 and thevessel 120. A valve 130 is provided in the line 129 so that the vessel120 may be isolated from the storage vessel 28 when the vessel 120 ischarged to the desired back pressure.

The mud discharge line 23 from the first or high pressure vessel 20communicates with the gas space in the vessel 120 above the liquid levelline. A pressure-reducing means 31 is disposed in the mud line 23 sothat the pressure in such line and the vessel 120 may be reduced to thedesired pressure. This pressure-reducing means 31 is preferably amultiple choke device so that the pressure may be reduced the desireddegree without an excessive increase in the velocity of the mud stream.It is noted that the pressure-reducing means 31 need not reduce thepressure of the mud stream to atmospheric pressure since a furtherpressure drop may be taken across the vessel 120 before the mud isdischarged through the line 123 into a storage vessel or pit.

The gas separated from the mud in the vessel 12% is conveyed therefromthrough the line 126 and valve 127 whereupon it may be flared orotherwise disposed of at a safe distance from the well. Th ud flowsthrough the vessel 120 in substantially a continuous manner so thatthere is little or no settling out of the cuttings or lost circulationmaterial from such mud stream. Since substantially all of the gas hasbeen removed from the mud stream by the time it passes through the valve124, there is little or no wearing of this valve due to the expansion ofentrained gas escaping from the mud stream as it passes through suchvalve, and since the pressure in the line 23 between the vessels 20 and120 is reduced by the pressure reducing means 31, there is little or nowearing of the mud control valve 24 due to the expansion of entrainedgas as the mud stream passes therethrough.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and various changes in the size,shape and materials, as Well as in the details of the illustratedconstruction, may be made Within the scope of the appended claimswithout departing from the spirit of the invention. As an example, andnot by way of limitation, the various components may be piped orconnected for reverse circulation, that is, the conduit 19 whichcommunicates with the vessel 20 would be connected to the drill pipe 11,and the pump discharge line 16 would communicate with the annulus 17 sothat the normal circulation is reversed in that the pump 13 pumps thedrilling fluid into the annulus 17 and thence outwardly through thedrill pipe 11 and into the conduit 19 and vessel 20.

What I claim is:

1. A method for controlling a well being drilled and having drilling mudcirculated therethrough, said method being carried out when pressureconditions which might cause a blowout are encountered, said methodcomprising,

passing returning mud into a pressure vessel, introducing pressure gasinto the vessel to charge the vessel to a pressure substantially inbalance with well pressure and thereby exerting back pressure againstthe drilling mud Within the well, said back pressure together with thehydrostatic pressure created by said drilling mud being of sufficientmagnitude to maintain the well under control. pumping drilling mud ofthe desired weight into the well to increase the weight of the drillingmud and hydrostatic pressure created thereby, varying gas pressurewithin the vessel to control said back pressure in relationship to thehydrostatic pressure created by the drilling mud being pumped into thewell whereby the hydrostatic pressure of the drilling mud columntogether with said back pressure are sufiicient to maintain the wellunder control during the pumping of said drilling mud, and discontinuingsaid introduction of pressure gas into said vessel when the hydrostaticpressure created by the column of drilling mud of increased weight issuflicient to again maintain the well under control. 2. A method forcontrolling a well being drilled and having drilling mud circulatedtherethrough, said drilling fluid having gas entrained therein, saidmethod being carried out when pressure conditions which might cause ablowout are encountered, said method comprising, passing returning mudinto a pressure vessel, introducing pressure gas into the vessel tocharge the vessel to a pressure substantially in balance with wellpressure and thereby exerting back pressure against the drilling mudwithin the well, said back pressure together with the hydrostaticpressure created by said drilling mud being of suflicient magnitude tomaintain the well under control, pumping drilling mud of the desiredweight into the well to increase the weight of the drilling mud andhydrostatic pressure created thereby, varying said back pressure inrelationship to the hydrostatic pressure created by the drilling mudbeing pumped into the well whereby the hydrostatic pres sure of thedrilling mud column together with said back pressure are sufiicient tomaintain the Well under control during the pumping of said drilling mud,continuously removing substantially all of the entrained gas in thedrilling mud from said mud as it passes under pressure through saidvessel, and discontinuing said introduction of pressure gas into thevessel when the hydrostatic pressure created by the column of drillingmud of increased Weight is sufiicient to again maintain the well undercontrol. 3. A method for controlling a Well being drilled and having -ahollow drill pipe and an annulus surrounding the drill pipe, one of thepipes and the annulus affording a flow conduit for mud delivered by apump and the other thereof affording a flow conduit for mud returning toan open pit, said method being carried out when pressure conditionswhich might cause a blowout are encountered, said method comprising,

passing returning mud into a separator upstream of the open pit,introducing gas under pressure into the separator for application ofback pressure against the drilling mud within the return flow conduit,said back pressure together with the hydrostatic pressure created bysaid drilling mud being of sufficient magnitude to maintain the wellunder control, pumping drilling mud of the desired weight into the muddelivery conduit to thereby increase the weight of the drilling mud andthe hydrostatic pressure created thereby, varying said back pressure inrelationship to the hydrostatic pressure created by the drilling mudbeing circulated into said mud delivery conduit whereby the hydrostaticpressure of the drilling mud 'column therein together with back pressureare sufiicient to maintain the well under control during the pumping ofsaid drilling mud, and discontinuing said introduction of pressure gasinto the separator when the hydrostatic pressure created by the columnof drilling mud of increased weight in the well is suflicient to againmaintain the well under control. 4. A method for controlling a wellbeing drilled and having drilling mud circulated therein, said methodbeing carried out when pressure conditions which might cause a blowoutare encountered, said method comprising, passing mud returning toward anopen storage pit first through a pressure vessel upstream of the openpit,

introducing pressure gas into the vessel for application of backpressure against the drilling mud contained within the annulus formed bythe exterior of the drill pipe and the bore of the well,

said back pressure together with the hydrostatic pressure created bysaid drilling mud being of suflicient magnitude to maintain the wellunder control and prevent a blowout through said annulus,

pumping drilling mud of the desired weight into the drill pipe toincrease the weight of the drilling mud contained therein and thehydrostatic pressure created thereby,

varying said back pressure in relationship to the hydrostatic pressurecreated by the drilling mud being circulated into said annulus wherebythe hydrostatic pressure of the drilling mud column in said annulustogether with said back pressure are sufficient to maintain the wellunder control during the pumping of said drilling mud and to prevent ablowout through said annulus.

and discontinuing said introduction of pressure gas into the vessel whenthe hydrostatic pressure created by the column of drilling mud ofincreased weight in said annulus is sufficient to again maintain thewell under control and prevent a blowout through said annulus.

5. A method for controlling a well being drilled and having drillingfluid therein, said method being carried out when pressure conditionswhich might cause a blowout are encountered, said method comprising,

initially charging a liquid gas separator with pressure gas to acontrolled pressure level,

placing said gas pressurized separator into communication with the welloutflow pipe for application of back pressure against the drilling fluidwithin the well, said back pressure together with the hydrostaticpressure created by said drilling fluid being of suflicient magnitude tomaintain the well under control,

pumping drilling fluid of the desired weight into the well to increasethe weight of the drilling fluid and hydrostatic pressure createdthereby,

adjusting gas pressure level within the separator for varying said backpressure in relationship to the hydrostatic pressure created by thedrilling fluid being pumped into the well whereby the hydrostaticpressure of the drilling fluid column together with said back pressureare sumcient to maintain the well under control during the pumping ofsaid drilling fluid,

and reducing the pressure level within the separator and the applicationof said back pressure when the hydrostatic pressure created by thecolumn of drilling fluid is suflicient. to again maintain the well undercontrol.

6. A method for controlling a well as set forth in claim together with,

first shutting in the well 'so that the Well is contained in theinterval required for mechanically connecting the separator to saidWell.

7. Amethod for controlling a well being drilled and having drillingfluid therein, said drilling fluid having gas entrained therein, saidmethod being carried out when pressure conditions which might cause ablowout are encountered, said method comprising,

initially charging a liquid gas separator with pressure gas to acontrolled pressure level,

placing said gas pressure separator into communication with the welloutflow pipe for application of back pressure against the drilling fluidwithin the well,

said back pressure together with the hydrostatic pressure created bysaid drilling fluid being of suflicient magnitude to maintain the wellunder control,

pumping drilling fluid of the desired weight into the well to increasethe weight of the drilling fluid and hydrostatic pressure createdthereby,

adjusting gas pressure level within the separator for varying said backpressure in relationship to the hydrostatic pressure created by thedrilling fluid being pumped into the well whereby the hydrostaticpressure of the drilling fluid column together with said back pressureare sufllcient to maintain the well under control during the pumping ofsaid drilling fluid,

continuously separating the gas entrained in said drilling fluid uponentrance thereof into the liquid gas separator,

utilizing said separated gas for maintaining said back pressure,

and reducing the pressure level within the separator and the applicationof said back pressure when the hydrostatic pressure created by thecolumn of drilling fluid is sufltcient to again maintain the well undercontrol.

8. An apparatus for controlling a well having drilling fluid thereincomprising,

a liquid gas separating vessel having an inlet line connecting saidvessel to said well for conveying the drilling fluid from the well intosaid vessel,

a liquid outlet line communicating with the interior of said vessel forremoving said drilling fluid from said vessel,

means coacting with said liquid outlet line for maintaining given limitsof liquid level in said vessel above said liquid outlet line whereby agas space is formed above said liquid level,

a gas outlet line communicating with said gas space within said vesselfor removing gas therefrom,

pressure responsive valve means in said gas outlet line arrange-d tothrottle said gas outlet line in response to selective pressures withinsaid gas space for maintaining a back pressure on the interior of saidvessel, and

an outside source of pressure gas connected directly into said gas spacefor charging said vessel with gas to a predetermined pressure.

9. An apparatus for controlling a Well having drilling fluid thereincomprising,

a first pressure vessel having an unrestricted inlet line connectingsaid vessel to said well for conveying the drilling fluid freely fromthe well into said vessel,

a second pressure vessel having a liquid outlet line communicating withthe interior of said second vessel for removing liquid from said secondvessel,

a conduit connecting the interior of said first vessel with the.interior of said second vessel for transferring drilling fluid fromsaid first vessel to said second vessel,

flow pressure-reducing means forming part of said conduit whereby thepressure in said second vessel is maintained at a point considerablyless than the pressure in said first vessel,

means coacting with said conduit for maintaining a liquid level in saidfirst vessel above the point at which said conduit communicates withsaid first 9 vessel whereby a gas space is formed above said liquidlevel,

a first gas outlet line communicating with said gas space within saidfirst vessel for removing gas therefrom,

means responsive to selected pressures within said first vessel andcoacting with said first gas outlet line for maintaining a relativelyhigh back pressure on the interior of said first vessel in excess ofwell pressure at said inlet,

means coacting with said liquid outlet line for maintaining a liquidlevel in said second vessel above the point at which said outlet linecommunicates with said second vessel whereby a gas space is formed abovesaid liquid level,

a second gas outlet line communicating with said gas space within saidsecond vessel for removing gas therefrom,

and means responsive to pressure within the second vessel and coactingwith said second gas outlet line for maintaining a back pressure on theinterior of said second vessel and at a level considerably less thansaid relatively high back pressure in said first vessel.

10. An apparatus for controlling a well as set forth in claim 9 togetherwith,

means for charging said first vessel with gas to a predeterminedpressure and from a source other than the well to be controlled.

11. An apparatus for controlling a well as set forth in claim 9 togetherwith,

a source of pressure gas other than gas from the well and control meansdelivering pressure gas from said source selectively to said firstvessel and to said second vessel and for charging the first vessel to ahigher 10 pressure than the pressure to which the second vessel ischarged.

12. A method of controlling a well being drilled and of overcoming thedisturbing effect on drilling mud pressures by incursion from earthformations such as might cause a blowout, said method comprisingconnecting the mud return line from the well with a liquid gas separatorunit having a level responsive valve in its liquid outlet and a variablevalved gas outlet, restricting said gas outlet and directing pressuregas from a source outside the well and into the separator to charge thesame to a pressure level for creating back pressure on the mud and ofsuch magnitude which combined with hydrostatic pressure maintains thewell under control, pumping mud of increased weight into the well,discontinuing the delivery into the separator and from said source asthe hydrostatic pressure increases, then reducing the restriction ofsaid gas outlet for reducing back pressure on the well until hydrostaticpressure alone is sufiicient to maintain the well under control.

References Cited by the Examiner UNITED STATES PATENTS 399,427 3/87Moore 166-8 1,938,019 12/33 Hild -25 2,082,329 6/37 Foran et a1 1752052,786,652 3/57 Wells 17525 OTHER REFERENCES Frank S. Bell, High-PressureDrilling and Blowout Prevention, The Oil and Gas Journal, Oct. 14, 1957.

BENJAMIN HERSH, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

1. A METHOD FOR CONTROLLING A WELL BEING DRILLED AND HAVING DRILLING MUDCIRCULATED THERETHROUGH, SAID METHOD BEING CARRIED OUT WHEN PRESSURECONDITIONS WHICH MIGHT CAUSE A BLOWOUT ARE ENCOUNTERED, SAID METHODCOMPRISING, PASSING RETURNING MUD INTO A PRESSURE VESSEL, INTRODUCINGPRESSURE GAS INTO THE VESSEL TO CHARGE THE VESSEL TO A PRESSURESUBSTANTIALLY IN BALANCE WITH WELL PRESSURE AND THEREBY EXERTING BACKPRESSURE AGAINST THE DRILLING MUD WITHIN THE WELL, SAID BACK PRESSURETOGETHER WITH THE HYDROSTATIC PRESSURE CREATED BY SAID DRILLING MUDBEING OF SUFFICIENT MAGNITUDE TO MAINTAIN THE WELL UNDER CONTROL.PUMPING DRILLING MUD OF THE DESIRED WEIGHT INTO THE WELL TO INCREASE THEWEIGHT OF THE DRILLING MUD AND HYDROSTATIC PRESSURE CREATED THEREBY,VARYING GAS PRESSURE WITHIN THE VESSEL TO CONTROL SAID BACK PRESSURE INRELATIONSHIP TO THE HYDROSTATIC PRESSURE CREATED BY THE DRILLING MUDBEIONG PUMPED INTO THE WELL WHEREBY THE HYDROSTATIC PRESSURE OF THEDRILLING MUD COLUMN TOGETHER WITH SAID BACK PRESSURE ARE SUFFICIENT TOMAINTAIN THE WELL UNDER CONTROL DURING THE PUMPING OF SAID DRILLING MUD,AND DISCONTINUING SAID INTRODUCTION OF PRESSURE GAS INTO SAID VESSELWHEN THE HYDROSTATIC PRESSURE CREATED BY THE COLUMN OF DRILLING MUD OFINCREASED WEIGHT IS SUFFICIENT TO AGAIN MAINTAIN THE WELL UNDER CONTROL.